Build a rat bike? Why spend time building what you can create simply by riding? Ride your bike, don't wash it. When it gets scratched up do a half-assed job of repairing the scratches... If something falls off that you don't need then don't put it back on. All my bikes eventually become rats. Real rats, not fake rats. Those are the only kind of motorcycles a man can truly love.
Then, in 20 or 30 years you can do a restoration.